高分子链的去拥挤转变及低温流动

简述了拥挤理论的基本原理,运用拥挤理论来说明高分子链间弱相互作用对高分子链所处的状态的影响,特别是对高分子玻璃化转变的影响.在实验中,采用固体核磁共振方法探测高分子的链间邻近度,并比较了不同链间邻近度的高分子样品在玻璃化转变温度以下的压力诱导流行行为,发现即使测试温度比高分子玻璃化转变温度低132℃,高分子链在压力下依...     

主链玻璃化转变区在室温附近的梳形聚合物电解质

主链玻璃化转变区在室温附近的梳形聚合物电解质＊齐力林云青夏永姚王佛松（中国科学院长春应用化学研究所长春１３００２２）关键词梳状高分子，固体电解质，离子导电性，玻璃化转变，分子运动＊１９９４－１０－３０收稿；１９９５－１２－１０修稿７３２高分子固体电解...     

高分子单链的研究进展

随着纳米科技在高分子领域的不断升温,高分子单链凝聚态的研究引起了人们的广泛重视。高分子单链以纳米尺度的微粒孤立存在,不存在分子链之间的几何缠结。本文综述了近年来国内外高分子单链的研究进展。首先介绍了高分子单链的主要制备方法如喷雾法、冷冻干燥法、微乳液聚合法、反向沉淀法以及表面扩展膜法,接着详细介绍了高分子单链的表征技术及高分子链构象的计算机模拟技术,最后介绍了高分子单链及单分子胶束在制备金属纳米粒子领域的应用,并展望了高分子单链的研究领域和方向。     

对聚合物玻璃化转变的几点新认识

基于聚合物玻璃化转变的定义,探讨了聚合物宏观单晶体和聚合物单链单晶的玻璃化转变问题,指出玻璃化转变的温度依赖性不服从普适的Arrhenius方程,可以把WLF方程看作是聚合物玻璃化转变的特有温度依赖关系。介绍了二维状态下聚合物可能的玻璃化转变。     

非晶物理框架下开展聚合物玻璃化转变教学的思考与探索

玻璃化转变是高分子物理教学中的重要内容.一些高分子物理教科书将聚合物玻璃化转变简单描述为玻璃到高弹态的力学转变,可能局限了学生对玻璃化转变重要科学问题认识的深度、广度和想象空间,甚至造成一些学生认为只有聚合物才存在玻璃化转变.笔者注意到了这一问题,考虑将聚合物玻璃化转变放在非晶物理框架下进行讲授;强调玻璃化转变是非晶物...     

红外光谱及二维相关光谱在讲解聚合物"玻璃化转变"概念的应用

玻璃化转变是聚合物的一种普遍现象,也是高分子物理教学过程中的一个重点内容.对玻璃化转变的本质进行深入透彻地讲解,有利于学生加深对高分子结构、高分子材料的性能和高分子链运动的统计学三个紧密相连部分的融会理解.针对目前教学过程中主要基于差示扫描量热法进行非晶态聚合物玻璃化转变温度概念讲解的不足,本论文交流了在教学过程中采用...     

聚合物薄膜玻璃化转变及其分子松弛行为的研究进展

随着纳米技术的发展,受限聚合物的玻璃化转变以及分子松弛行为受到了高分子物理学家的关注.由于纳米尺度效应,高分子薄膜的玻璃化转变以及分子松弛行为偏离于本体,呈现出尺寸依赖性.研究聚合物薄膜的玻璃化转变及其相关分子松弛行为对聚合物纳米材料的结构设计,进一步理解聚合物玻璃化转变的物理本质具有重要意义.本文总结了近20年来聚合物薄膜玻璃化转变行为的研究成果,介绍了薄膜分子松弛行为偏离本体的主要物理机制、聚合物薄膜分子运动能力的深度分布特征以及薄膜分子松弛行为的相关理论模型,并对该领域研究进行了展望.     

结合生活实际的《高分子物理》教学——以玻璃化转变为例

针对高分子物理内容较为抽象的特点,结合作者的教学实践,提出将高分子物理理论与生活中的高分子现象结合,以提高教学效果。以玻璃化转变的讲解为例,通过生活中的玻璃化现象引入玻璃化转变的概念,实现物理现象与理论知识的结合;进而在对玻璃化转变机理的学习中,引入自由体积理论在生活中的真实应用,消除学生对理论知识的陌生感。在这样的教学过程中,既可以克服学生对高分子物理的抽象感又可以培养学生的观察能力和思考能力,达到学以致用的目的。     

高分子单链凝聚态与线团相互穿透的多链凝聚态

高分子单链凝聚态由于链内链结构单元间存在范德华吸引作用,高分子链呈打圈链构象,而多链凝聚态由于链内链单元间的吸引作用被与相互穿透的近邻链的单元间吸引作用所屏蔽,高分子链呈高斯链构象.本文简要介绍单链凝聚态试样的制备方法,单链单晶体、单链玻璃体、溶胀的单链高弹态拉伸等的实验观察,并提出从单链凝聚态到多链凝聚态的转变过程问题,即高分子线团的相互穿透过程,目前还缺少基础了解.     

玻璃化转变的热力学理论错在哪里？

现行国内高分子物理学教科书上都介绍玻璃化转变的热力学理论,其把玻璃化转变描述成为一个二级相转变.但是现在人们已经普遍接受玻璃化转变的本质是一个动力学过程的观点.我们通过讨论玻璃化转变热力学理论的来历,试图弄清这一理论到底错在哪里.首先,该理论所基于的Kauzmann佯谬可能不是一个真正的佯谬;其次,半柔顺链高分子溶液的经典格子统计理论结果中所谓的熵灾难可能是出于对构型熵的错误理解所致.因此,把以上二者联系起来构成玻璃化转变热力学理论的基本假定就从根本上来说是不可靠的.     

A MONTE CARLO STUDY OF THE GLASS TRANSITION OF POLYMETHYLENE*

By this Monte Carlo simulation we studied the glass transition of polymethylene using themodified bond-fluctuation model combined with considering the rotational-isomeric state model. Theconfigurational properties in the polymethylene (PM) melts, such as the mean length, the mean energy perbond and the mean square radius of gyration were monitored. We found that the chains cannot be in theequilibrium states after a very long time when the temperature of the dense PM chains decreases to 120 K. Asthe melt vitrifies, these quantities gradually become independent of temperature in a narrow range. The glasstransition temperature T_g depends upon the chain length of PM chains, and extrapolation to (CH_2)_∞givesT_g~∞=212 K. The dynamics in the PM melts was also studied. It was found that the diffusion coefficients canbe described by the Vogel-Fulcher law and the Vogel-Fulcher temperature T_0 is 124 K. This method may beused to investigate the glass transition of other real polymer chains.     

Broadened glass transition in a liquid-crystalline polymer studied by thermally stimulated currents,AC dielectric,dynamic mechanical,and DSC methods

Thermally stimulated currents (TSC), a. c. dielectric, dynamic mechanical (DMTA), and differential scanning calorimetry (DSC) methods were used to study the glass transition in a thermotropic liquid-crystalline copolyester. All the techniques were consistent in the determination of the main glass transition temperature. Using the high sensitivity of the TSC thermal sampling method, it was shown that cooperative glass transition-like relax-ations occur down to 100°C below the main glass transition. DSC was sensitive only to a broadening of the glass transition to about ca. 30°C, so it was concluded that the thermal sampling method is sensing a very small fraction of cooperatively relaxing species which cannot be detected by DSC. Ac dielectric measurements and DMTA also indicated that the glass transition was broad, but difficulties with overlapping transitions prevented quantitative determination of the breadth of the glass transition. The results suggest that the broad glass transition, in this mostly amorphous LCP, is due to chemical heterogeneity of the copolyester chain. Other evidence indicates that the broadening is not due to the oriented nature of the glassy state. Some discussion is presented concerning how the heterogeneous nature of the LCP glass leads to compensation of the Arrhenius curves obtained by the thermal sampling method. © 1993 John Wiley & Sons, Inc.     

聚合物分子链的横截面积与分子链的运动

本文把单个分子链的横截面积与聚合物的玻璃化转变温度联系起来,发现对于所讨论的聚合物,考虑了分子链间的相互作用以后,上面二者之间有一一对应的关系。认为单个分子链的横截面积与聚合物分子链柔顺性有关。同时采用文献[17]的方法,得到了1,2-聚丁二烯的分子链的内旋转异构化能,比较所得结果,证实了上面的看法。     

木糖醇玻璃焓松弛的量热分析

为了考察木糖醇的玻璃化转变和焓松弛行为,寻求碳链长度对线性多元醇玻璃化转变和焓松弛行为的影响,利用差示扫描量热(DSC)技术测定了不同降温速率下木糖醇在玻璃化转变温度(Tg)前后的比热容(Cp),通过曲线拟合获得了TNM(Tool-Narayanaswamy-Moynihan)模型参数,并和其他多元醇类已有研究结果进行对照.结果表明,尽管TNM模型可以很好地重现不同降温速率体系的实验比热容数据,但模型参数并不是材料常数,而是和热历史有关,不同的降温速率对应不同的模型参数.指前因子(A)、非线性参数(x)和非指数参数(β)均随着降温速率的增加而降低,松弛活化焓(△h*)的变化趋势刚好相反.几种线性多元醇玻璃化转变和TNM模型参数的对照表明,玻璃化转变温度,松弛活化焓和动力学脆度(m)都随着烷基碳链长度的增加而增加.虽然非线性参数、非指数参数随碳链长度的增加有降低的趋势,但木糖醇展现出反常变化的情形.     

关于影响高分子材料玻璃化转变温度因素的教学分析

从《高分子物理》考试试题实例出发,抓住聚合物材料的"结构决定性能,并最终决定用途"这条主线,详述了链结构因素(主链和取代基)和分子间作用力对聚合物玻璃化转变温度(Tg)的影响,并结合不同高分子材料的用途进行分析,使学生真切了解到材料结构与性能及用途之间的关系。这种理论联系实际的案例教学法有利于加深学生对高分子材料的感性认识,引发学生学习的广泛兴趣,促使教师进行自我教育和提高业务水平,从而取得良好的教学效果。     

不同构型聚丙烯的玻璃化转变温度的分子模拟

应用分子力学和分子动力学的方法对3种不同构型聚丙烯高分子的玻璃化转变温度进行了模拟.用NPT(等温等压)分子动力学模拟获得聚丙烯(PP)在不同温度下的特征体积,通过对模拟得到的V-T做图,求得玻璃化转变温度,其结果与实验值吻合较好.并分析了聚丙烯主链柔顺性和立构规整度对高分子玻璃化转变的影响.     

Local segmental relaxation in bidisperse polystyrenes

Dynamic mechanical results are reported for segmental relaxation of monodisperse polystyrenes (PSs) with molecular weights of 0.7, 3, 18, and 104 kg/mol and bidisperse PSs created from blending pairs of these materials. The data for the monodisperse polymers confirm previous findings; namely, there is an increase in the glass‐transition temperature normalized temperature dependence of the segmental relaxation times (fragility) with increasing molecular weight, along with a breakdown of the correlation between the fragility and the breadth of the relaxation function. For both the monodisperse and bidisperse PSs, the glass‐transition temperature is a single function of the average number of chain ends, independent of the nature of the molecular weight distribution. It is also found that these materials exhibit fragilities that uniquely depend on the number‐average molecular weight, that is, on the concentration of chain ends. In blends with linear PS, cyclic PS with a low molecular weight behaves as a high polymer, similar to its neat behavior, reflecting the overriding importance of chain ends. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 2604–2611, 2004     

Preparation and thermal properties of graphene oxide/main chain benzoxazine polymer

Graphene oxide/polybenzoxazine nanocomposites are prepared using main chain benzoxazine polymer (MCBP) via a solvent casting method from different organic solvents. The addition of graphene oxide to the polymeric matrix leads to a gradual decrease in the glass transition temperature of the polymeric matrix. This drop is attributed to the reactive nature of graphene oxide, which undergoes exothermic thermal de-oxygenation before the onset of polybenzoxazine ring opening polymerization upon curing of the nanocomposites. Additionally, it is reported that the glass transition of polybenzoxazine films cast from different solvents depends on the nature of the solvent.     

A theoretical interpretation of free volume at glass transition

We device a relaxed lattice model (RLM) to study the mechanism of glass transition,which unifies the cageeffects from particle-particle interaction and entropy.By analyzing entropy in RLM with considering the influence of interactions on equilibrium,we demonstrate that glass transition is a second-order phase transition.For a perfect onedimensional linked particle system like linear polymer under normal pressure,the free volume at glass transition is rigorously deduced out to be 2.6％,which provides a theoretical basis for the iso-free volume of 2.5％ given by Willian,Landel and Ferry (WLF) equation.Extending to system with dead particles linked with higher dimensions like branched or cross-linked chains under positive or negative pressure,free volume at glass transition is varied,based on which we construct a phase diagram of glass transition in the space of free volume-dead particle-pressure.This demonstrates that free volume is not the single parameter determining glass transition,while either dead particles like cross-linked points or external force fields like pressure can vary free volume at the glass transition.